Vulcanization of rubber coverings for electrical conductors



UNITED STATES PATENT. OFFICE.

JOHN J. C. SlVllTH AND MICHAEL SMITH, OF PASSAIG, NEXV JERSEY.

VULCANlZATlON 0F RUBBER COVERINGS FOR ELECTRICAL CONDUCTORS.

SPECIFICATION forming part of Letters Patent No. 317,587, dated May 12,1885.

Application filed August 1, 1884. (Specimens.)

To a. whom it may concern:

- Be it known that we, JOHN JosErH CHARLES SMITH and MIcHAEL SMITH,citizens of the United States, residing at Passaic, in the county ofPassaic and State of New Jersey, have invented certain new and usefulImprovements in Vulcanizing Rubber or other Vulcanizable InsulationCompounds used as Coverings of Electric Conductors, of which thefollowing is a specification.

The object of this invention is to vulcanize such coverings in such amanner as to avoid the detrimental effects of moisture on theinsulating-coverings of electric conductors while such coverings are inprocess of vulcanization.

\Ve have found that any moisture which may come in direct contact withthe insulatingcovering of electric conductors while such covering isbeing vulcanized will seriously affect and impair, if it does notdestroy, theinsulating qualities of the covering.

In order that those who are skilled in the art of producinghighly-insulated electric conductors may fully understand the noveltyand importance of our invention, we will first relate some facts whichcame within the scope of our observation while going through a longseries of experiments on an extensive scale for the purpose of producinga high insulation of electric conductors by the use of avulcanizedrubber compound.

Under the principal methods now used to vulcanize the covering ofelectric conductors, either the insulating compound is made so that itmay be vulcanized in a dry-heat chamber, where no pressure can beapplied to the compound during the process of vulcanization, or thecovered conductors are packed in dry soapstone-powder and are placed ina vulcanizingvessel, where steam is admitted, which produces therequired heat and pressure at the same time. The last-named is verytroublesome on account of the difficulty of properly packing a longpiece of insulated wire in the soapstone. In both cases the compoundsused as insulating-coverings are made up with a view to being of suchnature that they can be vulcanized in either one or the other way, and

therefore are not of such high insulating quali- 50 ties as theyotherwise might be.

Many slight modifications of these systems are in use; but theprinciples remain the same.

lVhile carrying on our experiments we used both of these systems andmanyof the sundry modifications in vogue; but found invariablythattheinsulation resistance of the compounds was very much lower aftervulcanization than before, and too often was lost altogether. By closeobservation we found that the compound absorbed more or less moistureduring vulcanization by one or the other mode. \Vhen vulcanized in dryheat without pressure, the compound was full of fine pores unless it wasmixed in considerable quantity with heavy ingredients not suitable forproducing high insulation. Such observation led us to adopt our presentnew method,the principle of which is to inclose the insulating-coveringin 2. her metical envelope, through which moisture cannot penetrateunder pressure, and to vulcanize the covering undersuch aprotection.This effectually prevents moisture from coming in contact with thecompound while it is being vulcanized.

\Ve have carried our invention into effect with complete success in thefollowing manner: lVe lay a sheet of the insulating compound firmly on along sheet of heavy tin-foil, and then out both in long narrow strips,in the manner described by J. J. C. Smith in his Patent No. 276,725,dated May 1, 1883, with reference to cutting in long strips combinedsheets of insulating and fibrous material. Such strips of tin-foil, incombination with the vulcanizable insulating material, we lay on thewire by means of the covering-machine described andclaimed by the saidJ. J. G. Smith in his Patent No. 276,72l, dated May 1, 1883.

Under our present invention the tin-foil answers the same purpose as thefibrous sheet in affording facility for laying and pressing the coveringclosely on the wire; but in addition to this it serves the veryimportant purpose of providing an impervious envelope for the insulatingcovering, and protecting it fully against the influence of moistureduring vulcanization, thus permitting the direct pressure and heat ofsteam without injurious effect. It also differs from the fibrouscovering in that it does not become inseparably incorporated ICOmegohms.

with the insulating-covering. Ithas long been known th at allvuleanizable compounds become much better and of closer texture ifvulcanized under pressure. Many cannot be vulcanized in a solidcondition without pressure. Others which can be vulcanized in dry heatwithout pressure possess this capability because heavily loaded withingredients injurious to a good insulation.

WVhen the insulating-cover is to be vulcanized, we coil the covered wireon a large but light metallic reel in two or three layers. This reel isso arranged that it may be put readily in and out of the vulcanizer, andthat it can be revolved horizontally in the vulcanizer while the same isclosed and in operation. The revolving of the reel is accomplishedby'means of a shaft extendingthrough a stuffingboX in the head of thehorizontal vulcanizer and provided with a driving-gear on the outl hereel may be advantageously made to contain about two miles of wire atone charge, and is rotated for the purpose of continually changing theposition and weight of the wire and its covering, which keeps the wirecentral in the covering while it is softened by heat before thevulcanization takes place.

Then the vulcanization is completed, the wire is taken out, and the tinenvelope, having performed its function, is removed from theinsulatingcovering, leaving a smooth and dense surface.

To illustrate the importance of a tin-foil or other metallic foilcovering on the outside of the insulation-covering as a protectiveenvelope during vulcanization, we will state the results of a number ofexperiments in vulcanization by other methods,and the results when weused the metallic envelop An insulation compound such as is used in oneof the best-known manufactories of lllSlllated wire, and which wedesignate as compound No. 1, was laid one twenty-fourth of an inch thickon one thousand feet of No. 14 copper wire. Before vulcanization theinsulation resistance of the cover was one hundred and eight megohms. Itwas then vulcanized in a dry-heat chamber without pressure. Atervulcanization the insulation resistance of the covering stood onlytwenty-seven and onehalf megohms, and it fell to fifteen megohms afterimmersion in water for three days. This proved that fine pores must haveformed during vulcanization, which absorbed moisture, thereby injuringtheinsulation. Another one thousand feet of wire, covered with the samecompound No. 1 one twenty-fourth of an inch thick, showed one hundredand twelve megohms before vulcanization. It was vulcan- 7 ized in a drysoapstone-powder bed carefully packed and heated. under steam-pressure.After vulcanization the insulation resistance of this covering wasthirty-seven and one-half Three days immersion in water brought it downto twenty-three megohms. A third piece one thousand feetlong was covl Iin J. J. C. Smiths application filed the 7th of l l l l l ered with thesame compound No. 1 to the same thickness, and was protected by what iscommonly called a waterproof tape. This piece was vulcanized in steamunder pressure generally cured. After vulcanization it in less thanthree hours immersion in water it came down to one-half megohm. A fourthpiece of one thousand ,feet was covered with I the same compound thesame thickness, but protected by our metallic envelope. Beforevulcanization this piece indicated one hundred and thirteen megohmsinsulation resistance. It was vulcanized in steam under sixty- Aftervulcanization this pOLllldS pressure. picce'indicated an insulationresistance'of one -three megohms, which showed a great increase of theinsulation resistance. Three days immersion in water proved it to ,beunalterable.

The rubber compound described and claimed hundred and sixty April, 1884,showed still more remarkable results. This compound is absolutelywaterproof and one of the best insulators. It was laid on one thousandfeet of No. 14 copper wire, one twenty-fourth of an inch thick, the samethickness as in the previous experiments with compound No. 1. When raw,this compound showed an insulation resistance of two hundred and fortymegohms. After vulcanization in dry soapstone-powder under pressure ofsteam, it showed an insulation resistance of ninety-two megohms, fallingto fortyseven after three days immersion. A second piece covered withthe said Smiths compound and with water-proof tape as a proteetion,andvulcanized in steam under pressure, showed only seventy-two megohmsinsulation after vulcanization, -falling to forty megohms after threedays immersion in water. A third piece of one thousand feet of wirecovered with Smiths compound, but protected by our metallic envelope,was vulcanized in steam under pressure. After vulcanization it showed aninsulation resistance of five hundred and seventy megohms. Immersion inwater for weeks had no influence upon it. Repeated trials with the samecompounds and many others showed corresponding results, proving the factthatif an electric conductor insulated with a vulcanizable compound iscovered with a metallic envelope in the manner described, and'isvulcanized under such a protection,the insulation resistance of thecovering is very much improved. All the named trials were made withequal accuracy, and all tests and measurements taken with the mostsensitive instruments and galvanometers.

In order to avoid any possibility of mistake about one or the othercompound,we took hardrubber or ebonite compound, which is known as oneof the best insulators.

first sample vulcanized showed an insulation resistance of ninety-sevenshowed only seven megohms insulation, and

in the manner in which soft-rubber goods are 1 30 It was laid on thewire the same thickness as the other. The in dry soapstone megohms, butfell to forty after immersion. The second example vulcanized in steamshowed only one-half megohm after vulcanization. The third sample wasvulcanized under the protection of the metallic envelope. Aftervulcanization .it stood two hundred and eighty megohms, and did notchange by immersion in water. These trials proved conclusively that allvulcanizable compounds suffer in their insulating qualities whenVl1lC2L11-,

ized in such a manner that moisture may come in contact with thematerial lll'PIOCGSS of vulcanization. If vulcanized in dry heat orsoapstone, it suffers from want of pressure on the compound, and a fineporous formation takes place, or the compound must be so much loadedwith other ingredients as to affect its insulating qualities.

"We are well aware that tin-foil or other metallic sheets are used inthe manufacture and vulcanization of rubber goods to obtain smoothsurfaces,or to keep the rubber in shape, or to facilitate molding andpressing in special forms; but it will be apparent that the imperviousmetallic envelope performs an essentially different and novel functionin our process of vulcanizing insulation-coverings of electricalconductors. i

We use the tin-foil or other pliable metal sheets as an envelope thatcannot be penetrated by moisture, so that we may fully protect ourinsulating compound against the detrimental influence of moisture whileit is vulcanized, permitting us to use direct action of steam as thebest and most convenient medium to produce the required heat andpressure at the same time.

What we claim as new, and by Letters Patent, is-

The mode or process herein described of vulcanizing theinsulating-covering of electrical conductors, the same consisting inenveloping the covered wire in a tight and impervious cover of tin-foilor other pliable metal, and subjecting it to the combined andsimultaneous action of heat and pressure.

.T. J. 0. SMITH. MICHAEL SMITH.

lVitnesses:

JOHN B. PUDNEY, EUGENE 0. SMITH.

desire to secure

